In selective catalytic reactors (SCRs), a catalyst is utilized to remove NOx from combustion gases. Because the catalyst is most effective in a temperature range of about 315-425° C., during start-up of a SCR the catalyst is cold and can require as much as 12 hours or more for the plant to reach the required temperature before ammonia can be injected. In addition, new regulations have placed additional pressure on owners of SCRs to reduce plant emissions to low levels even during start up periods.
A schematic of a portion of a typical coal-filed power plant 100 is shown in FIG. 1, which lacks any control over the temperature of the catalyst and thus the catalyst's temperature is dependent on the firing and heat absorption conditions in the furnace 102, superheaters, and economizer regions 106 in the boiler 108. For these reasons, ammonia 110 is generally not injected into the SCR 112 until the catalyst in the SCR 112 reaches a temperature of at least 250-315° F. Below this temperature, reactions generally will not occur and the ammonia would be wasted and would pass through to the atmosphere.
Although it is known to preheat oxidizing catalysts for fuel reforming, such as that described in U.S. pat. publ. no. 2001/0047620 to Ichikawa et al. (publ. December 2001) and U.S. pat. publ. no. 2009/0223861 to Sugiura et al. (publ. September 2009), such processes are specific to fuel reforming rather than reducing catalysts for use in selectively removing reactive gases from a combustion flue gas. Ichikawa and all other extrinsic materials discussed herein are incorporated by reference in their entirety. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
Thus, there is still a need for systems and methods for reducing the start-up time in a flue gas conditioning process.